Ultrasound Scans and What They Monitor

Ultrasound imaging uses high-frequency sound waves to create real-time images of the developing baby inside the womb. It is a safe, non-invasive, and widely used diagnostic tool in prenatal care. Unlike X-rays, ultrasound does not involve radiation, making it suitable for repeated use throughout pregnancy when medically indicated.

In India, ultrasound scans during pregnancy are regulated under the Pre-Conception and Pre-Natal Diagnostic Techniques (PCPNDT) Act, which prohibits the use of prenatal imaging for sex determination. All scans must be conducted by registered practitioners at registered centres, and the purpose is strictly medical assessment of fetal and maternal health.

Obstetricians in Visakhapatnam typically recommend a series of ultrasound scans at key stages of pregnancy. Each scan has a specific purpose and provides information that helps guide the management of the pregnancy. Understanding what each scan monitors can help expectant mothers approach them with confidence.

The first ultrasound is usually performed between 6 and 10 weeks of pregnancy. Known as the dating scan, its primary purpose is to confirm the pregnancy, determine the gestational age, and estimate the due date. The scan also checks for the fetal heartbeat, which is a reassuring sign of a viable pregnancy.

This early scan can identify whether the pregnancy is located within the uterus or if it is an ectopic pregnancy, which requires immediate medical attention. It can also reveal multiple pregnancies, such as twins, which require specialised monitoring. The crown-rump length of the embryo is measured to establish an accurate gestational age.

Between 11 and 14 weeks, a nuchal translucency scan may be performed. This measures the fluid-filled space at the back of the baby's neck and, combined with blood test results, helps assess the risk of chromosomal abnormalities. This scan is optional but recommended by many obstetricians as part of first-trimester screening.

The anomaly scan, also known as the mid-pregnancy scan or level II ultrasound, is typically performed between 18 and 22 weeks. It is one of the most detailed scans during pregnancy and examines the baby's anatomy in considerable detail. The brain, heart, spine, kidneys, limbs, and other organs are systematically evaluated.

This scan also assesses the position and condition of the placenta, the amount of amniotic fluid, and the umbilical cord blood flow. A low-lying placenta identified at this stage is often monitored with a follow-up scan later in pregnancy, as it frequently moves to a normal position as the uterus grows.

The anomaly scan provides important information that helps doctors plan for any additional care the baby may need at birth. If structural abnormalities are detected, the healthcare team can counsel the parents, arrange specialist consultations, and ensure that delivery takes place at a facility equipped to manage the specific condition.

In the third trimester, ultrasound scans focus on assessing fetal growth, position, and preparation for delivery. Growth scans estimate the baby's weight, measure the head circumference, abdominal circumference, and femur length, and compare these measurements against standard growth charts. This helps identify babies who are growing too slowly or too rapidly.

The baby's position in the uterus becomes increasingly important as the due date approaches. A head-down position is ideal for vaginal delivery, while a breech or transverse presentation may require special manoeuvres or a planned caesarean section. Ultrasound confirms the baby's lie and helps the doctor plan accordingly.

Amniotic fluid volume is re-evaluated in the third trimester. Both too much fluid (polyhydramnios) and too little fluid (oligohydramnios) can indicate underlying issues that need medical attention. Doppler ultrasound may also be used to assess blood flow through the umbilical cord and placenta, providing additional information about the baby's well-being.

Doppler ultrasound is a specialised technique that measures the speed and direction of blood flow in the umbilical artery, uterine arteries, and fetal vessels. It is particularly useful in high-risk pregnancies where there are concerns about placental function, fetal growth restriction, or maternal conditions such as preeclampsia.

Abnormal Doppler findings may indicate that the baby is not receiving adequate oxygen and nutrients through the placenta. Based on these findings, the doctor may recommend more frequent monitoring, hospitalisation, or early delivery if the baby's health is at risk. Doppler assessment is a valuable tool for managing complicated pregnancies.

Ultrasound has been used in obstetric care for decades and is considered safe for both mother and baby when performed by trained professionals for medical purposes. There is no evidence of harmful effects from diagnostic ultrasound at the intensity levels used in clinical practice. However, scans should be performed only when medically indicated, not for non-medical purposes such as keepsake images.

The number and timing of scans vary depending on the individual pregnancy. Uncomplicated pregnancies may require only two or three scans, while high-risk pregnancies may need more frequent monitoring. The obstetrician determines the scan schedule based on the clinical situation, and mothers should follow this guidance to ensure optimal care for themselves and their babies.